The present invention relates to the handling of thick, viscous or thixotropic materials, and more particularly to the reclamation from storage lagoons of dry, semi-dry or nearly gelatinous sludge produced as a by-product of various manufacturing operations and/or various conventional waste sludge sewage treatment processes.
Although the actual chemical composition of the materials to be removed from catch basins or lagoons will vary from location to location, normally such materials have been deposited in a liquid or semi-liquid state and have been stored in such lagoons or catch basins for a considerable period of time, which storage results in the thickening of the material due to decreasing moisture content. Moisture content may range from about 99.5% to as low as 60%, but commonly in the range of 92% to 85% after several years of aging in the lagoon. As described in U.S. Pat. No. 3,796,658, at this common moisture level the sludge does not behave as a fluid, but rather, resembles a heavy viscous or soft gelatinous material having thixotropic tendencies.
The problems which are encountered in cleaning lagoons or catch basins of this type are aggravated by the fact that (depending upon the constituency of the waste products disposed therein) chemical reactions, microbic growth, local geologic characteristics including soil porosity and water table levels, and the particular design and construction of the lagoon or catch basin to be cleaned result in extremely discontinuous deposits of materials to be removed. For example, depending on exposure, porosity, dwell time in the lagoon, the varying nature of the substances charged into the lagoon from year to year, and many other factors, the consistency and handleability of waste material to be removed from within any given lagoon, much less from one lagoon to the next, will vary markedly by depth and region.
Conventionally, lagoons, catch basins and similar installations have been brought from the dry, semi-dry or gelatinous state to a pumpable state by injecting fluid such as water into the material in order to increase the moisture content of the material to a point where the material is pumpable, at which time a conventional pumping apparatus is utilized to pump the resultant sludge to rail tank cars or trucks. It may then be removed from the lagoon for transport to a suitable dump site or other disposal facility. As further described in U.S. Pat. No. 3,796,658, it is not practical to attempt to pump even gelatinous or semi-liquid sludge which does not flow evenly since a pump placed in the sludge simply pumps out a small area or cavity and ceases to receive additional input after the immediately adjacent material is removed. Adding water to the sludge reduces the aforementioned flow and pumping problems to some extent, but the increased total weight and volume of the resulting material increases shipping and disposal costs. Since the material in the lagoons has normally lost moisture and thickened with age, it is desirable to transport the material in a thickened condition or with the addition of only the minimum amount of water necessary to facilitate pumping.
U.S. Pat. No. 1,331,239 illustrates an early portable pumping apparatus intended for use for the evacuation of cesspools, sumps, basins or depressions or excavations in which the character of the contents is such that they should not pass through the pump without partial separation of the solids contained in them. A multi-chambered settling tank is utilized in order to allow liquids to be separated from the collected solids and to be sprayed as desired. See also, U.S. Pat. No. 1,344,710 which appears to disclose an improvement over the device disclosed in U.S. Pat. No. 1,331,239 wherein water which has been separated from the solids is recirculated into the catch basin 3 and is used to supply ejector 4. A similar system appears to be disclosed in U.S. Pat. No. 1,343,471. Although the travelling apparatus for cleaning sewer basins and the like disclosed in these three patents first became known in approximately 1920, the method disclosed therein for cleaning catch basins and the like has not changed substantially in the intervening 56 years. See, for example, U.S. Pat. No. 2,753,877 dated July 10, 1956 which discloses injection of water into a sandpit to agitate the sand into a suspension and subsequent pumping of the suspension into a settling tank in which the sand is allowed to settle out and the water recirculated for subsequent use to further agitate material contained within the basin.
Also note U.S. Pat. No. 3,262,571, dated July 26, 1966 wherein a mobile unit is disclosed for use in cleaning out catch basins and the like. The specification of this patent states:
"In cases where the debris is substantially dry, the eduction unit deposits a fluid into the sewer or catch basin in order to loosen the debris and to mix it with a fluid so that it will be easily sucked up by the eduction unit. The mixture is deposited in the settling tank where the heavier debris falls to the floor. The fluid with the lighter debris in suspension passes through a series of baffles and/or strainer so that the lighter debris is removed from the fluid. The fluid which is now relatively free of debris may be redeposited into the catch basin and reused to loosen the mix with additional debris. Thus, the fluid is recirculated. An example such as the eduction unit is shown in U.S. Pat. No. 2,010,538, dated Aug. 6, 1935." Specification U.S. Pat. No. 3,262,571, column 1, lines 17-30.
While relatively sophisticated methods have been developed in order to process conventional sludge at treatment plants, such instrumentation has not been applied to dewatering and/or treating materials collected during cleaning catch basins. While it might initially appear that a system such as that disclosed in U.S. Pat. No. 3,630,365 might be directly applicable to the art of catch basin or lagoon cleaning, such systems are intended to be used to process conventional sludge which, in comparison to catch basin waste materials, is an extremely homogeneous material of known constituency and chemical and/or bacterial composition. Additionally, such systems are fed with a liquid sludge containing a relatively small solids content thereby enabling the construction of a system which is efficient for its intended purpose, but which could not adequately process waste materials as directly collected from conventional lagoons or catch basins. Other patents generally disclosing systems, methods and equipment for processing sewage sludge and similar types of waste are U.S. Pat. Nos. 3,045,827, 3,275,547, 3,248,323, 3,226,317, 3,732,697, 3,720,608, 1,696,014, 2,228,017, 3,577,341, 3,739,912, 2,120,658, 2,391,494, 2,359,748 and 3,879,285.
Other patents disclosing the use of a settlement or recirculation concept include U.S. Pat. Nos. 1,873,598, 3,317,049, 2,240,167 and 3,616,917.
Subsidiarily, many processes and/or chemical reagents have been developed which are useful generally in combination or as a part of various dewatering processes. See, for example, U.S. Pat. Nos. 3,300,407, 3,897,333, 3,849,307, 3,409,546, 3,514,398, 3,720,609, 3,841,102, 3,899,419, 3,907,677 and 3,806,450.